Implementation of leaky bucket rate limiter in TS

leaky-bucket-rate-limiter.ts

/*
  The algorithm is simple: 
  Assume a bucket that can hold a limited amount of water (requests). Over time, water leaks out at a fixed rate,
  creating space for new water. A new request (water) is only accepted if there is enough free space in the bucket;
  otherwise, it is denied.
*/
class LeakyBucketRateLimiter {
  private bucketCapacity: number;
  private currentBucketSize: number;
  private bucketLeakRate: number;
  private lastUpdate: number;

  constructor(capacity: number, leakRate: number) {
    // Maximum capacity of the bucket (requests allowed)
    this.bucketCapacity = capacity;
    // Currently, consumed bucket size
    this.currentBucketSize = 0;
    // The rate at which the bucket is leaking
    this.bucketLeakRate = leakRate;
    // Timestamp of last update
    this.lastUpdate = Date.now();
  }

  private leak(): void {
    const timeNow = Date.now();
    const timeSinceLastUpdate = (timeNow - this.lastUpdate) / 1000; // seconds
    const tokensToLeak = timeSinceLastUpdate * this.bucketLeakRate;
    this.currentBucketSize = Math.max(0, this.currentBucketSize - tokensToLeak);
    this.lastUpdate = timeNow;
  }

  public consume(requests = 1): boolean {
    this.leak();
    // Only allow if current bucket size + requests will not overflow the bucket
    if (this.currentBucketSize + requests <= this.bucketCapacity) {
      this.currentBucketSize = this.currentBucketSize + requests;
      return true;
    }
    return false;
  }
}

// Test cases
const testLimiter = new LeakyBucketRateLimiter(5, 1);

// Should not allow more requests than capacity
console.assert(testLimiter.consume(6) === false, "Deny requests if over capacity);

console.assert(testLimiter.consume() === true, "First request should be allowed");
console.assert(testLimiter.consume(4) === true, "Should allow up to capacity");
console.assert(testLimiter.consume(1) === false, "Deny request exceeding capacity");
setTimeout(() => {
  console.assert(testLimiter.consume() === true, "After leakage, request should be allowed");
}, 1500); // The rate is 1req/sec.